Changes Of Gene Expression Of Myocardial Cytoskeletal Protein In Endotoxemic Rats

Lipopolysaccharide(LPS),the cytoderm component of Gram-negative bacteria,is a critical harmful factor to organism,it has been found that release of LPS into blood flow by bacteria in endotoxemia,sepsis and septic shock can activate immune system and inflammatory reaction which will injure organism seriously;but the pathophysiology of sepsis or LPS-induced tissue injury and organ dysfunction remains controversial. LPS can also decrease myocardial contractility and cause cardiac dysfunction.But it's not clear how LPS injure myocardial tissue and decrease the heart function.As a major component of myocardial cells,cytoskeleton proteins play important role in the maintenance of cells shape and framework,material transportation and myocardial contractility.Our recent studies suggest that changes of myocardial cytoskeleton actin and desmin may be related with the decrease of myocardial contractility in LPS-treated rats.The aim of this study is to observe the changes of gene expression of myocardial cytoskeleton proteins in LPS-treated rats and so to investigate the mechanism of LPS on heart function.In the experiment,rats were treated with Salmonella lipopolysaccharide(10mg/kg,body weight) to reproduce the model of endotoxemia.The heart function parameter,such as heart rate(HR),left ventricular end diastolic pressure(LVEDP),left ventricular systolic pressure(LVSP),±dp/dt max,were monitored continuously for 24 to 72 hours.The concentration of creatine kinase(CK) in serum and the mRNA content of cytoskeletal protein(Actin,Tubulin,Desmin) in myocardial cells were measured.The results show that HR,LVEDP,LVSP,and +dp/dt max reduced significantly after LPS treatment.But there was no significant changes about—dp/dt max.We also found that the concentration of CK was not decreased remarkably.The pathological examination show that there are apparent capillary hemorrhage in myocardium of rats treated with one dosage of LPS(10 mg/kg, body weight) for more than 8 hours.The typical myocardial transverse striation was not seen clearly,toxic granulation appeared in cytoplasm, and a few apoptosis cell could be seen.And there were no obvious histological improvement for the damaged myocardial cells in rats even survived for 48 hours.Electron microscope examination shows that myocardial fiber direction is changed,its transverse striation become blurry and mitochondrial crista declined in rats with LPS treatment from 4h to 24h..The mRNA content of actin,tubulin and desmin of cadiocytes in endotoxemic rats were measured with RT-PCR method as comparison with GAPDH mRNA.By electrophoresis with horizontal 2%agarose gel and fluorescence optical density scan analysis,we found that the mRNA of actin was reduced significantly 8hours after LPS treatment,and that of tubulin was decreased significantly 24 hours after LPS treatment.But desmin mRNA was not changed obviously.The above results indicate that LPS may in vivo damage the heart function seriously,especially decrease the myocardial contractibility, but the diastolic function of heart was not influenced remarkably.LPS may also induce a obvious histological and morphological injury of myocardial subcellular structure,including mitochondrial damage and myocardial striation destroyed.And gene expression of myocardial cytoskeleton protein(actin and tubulin) may be down-regulated significantly by LPS.It suggest that reduction of myocardial contractibility may be related to the injury of myocardial cytoskeletal structure by LPS treatment.